Gallium nitride materials include gallium nitride (GaN) and its alloys such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN). These materials are semiconductor compounds that have a relatively wide, direct bandgap which permits highly energetic electronic transitions to occur. Such electronic transitions can result in gallium nitride materials having a number of attractive properties including the ability to efficiently emit blue light, the ability to transmit signals at high frequency, and others. Accordingly, gallium nitride materials are being widely investigated in many microelectronic applications such as transistors, field emitters, and optoelectronic devices.
In many applications, gallium nitride materials are grown on a substrate. However, differences in the properties between gallium nitride materials and substrate materials can lead to difficulties in growing layers suitable for certain applications. For example, gallium nitride (GaN) has a different thermal expansion coefficient (i.e. thermal expansion rate) and lattice constant than many substrate materials including sapphire, silicon carbide and silicon. These differences in thermal expansion and lattice constant may lead to the formation of defects (e.g., dislocations) and cracking, as well as warping (e.g., bowing) of the overall structure.